The present invention relates to industrial process control or monitoring systems. In particular, the present invention relates to process variable transmitters configured to sense process variables in such systems.
Process variable transmitters are used in industrial process control environments to monitor process variables. Such transmitters couple to a process fluid and provide measurements related to the process. Process variable transmitters can be configured to monitor one or more process variables associated with fluids in a process plant, such as slurries, liquids, vapors and gases in chemical, pulp, petroleum, gas, pharmaceutical, food and other fluid processing plants. Example monitored process variables include pressure, temperature, flow, level, pH, conductivity, turbidity, density, concentration, chemical composition or other properties of fluids. Typically, the process variable transmitters are located at remote locations, usually in a field, and send information to a centralized location such as a control room. Process variable transmitters sense process variables in a variety of applications, including oil and gas refineries, chemical storage tank farms, or chemical processing plants. In many instances, this requires the process variable transmitters to be located in a harsh environment.
Some types of process variable transmitters include a housing divided into two separate compartments. One compartment contains electrical circuitry and the other compartment contains a terminal block used to couple to a process control loop. One such configuration is shown in U.S. Pat. No. 5,546,804. In such a configuration, the compartment which contains the terminal block may collect moisture due to condensation, leaks, or other sources. Such moisture may cause errors in data transmitted by the process variable transmitter and may even lead to ultimate failure of the device. One known technique to detect such moisture is by monitoring changes in electrical characteristics of the process control loop. Such techniques are shown and described in, for example, US Publication No. 2011/0010120, to Wehrs et al., entitled PROCESS VARIABLE TRANSMITTER WITH TWO-WIRE PROCESS CONTROL LOOP DIAGNOSTICS and assigned to Rosemount Inc.